Stimulation of the growth of muscle cells in tissue culture by hormones with established anabolic effects in whole animals will be investigated. The hormones to be studied are growth hormone, insulin, and somatomedin. Relationship of growth-promoting effects to physiological levels of the hormones will be considered. Both myoblasts and myotube cultures will be used, and comparisons of hormone effects at these two stages of muscle development will receive particular attention. BIBLIOGRAPHIC REFERENCES: Powers, M. Linda, and Florini, James R., A Direct Effect of Testosterone on Muscle Cells in Tissue Culture, Endocrinology 97: 1032-1036 (1975). Florini, J. R., Geary, S., Saito, Y., Manowitz, E. J., and Sorrentino, R.N., Changes in Protein Synthesis in Heart, p 149-162 in Explorations in Aging (V.J. Cristofalo, J. Roberts, and R. C. Adelman, Eds.) Plenum New York, 1975.